Rethinking the two-fluid model of two-phase flow

Abstract

Forbetter or worse, the two-fluid model (TFM) has become the basis of numericalcodes for the thermohydraulics of nuclear reactors and accident analysis, evenif its completeness is still disputed. The main source of controversy is that the TFMmomentum conservation equations are elliptic (i.e., the ill-posedness problem),which, among other things, causes the solutions to short wavelengthperturbations to have an infinite growth rate. This paper presents recentresearch advances on the matter leading to aphysically-based method for deriving well-posed instances of TFM using thevariational principles of field theory. The new formulation leads to a novelrepresentation in which the drift flux is endowed with its own conservationequation, and well-posed TFM cases can be obtained by modeling the storage andexchange of kinetic energy caused by the interaction between fluids, such aswakes and eddies. The new methodology is a promising framework for newgenerations of thermal-hydraulic and nuclear reactor safety codes.